Field of the Invention
The invention relates to a device and a method for regulating a pressure in a high pressure accumulator for fuel injection systems having a pressure adjusting element which has a shut-off element which is actuated by an electromagnetic drive.
In the field of fuel injection systems for internal combustion engines, high pressure accumulator configurations which comprise essentially a high pressure pump, a high pressure accumulator, injection valves and an electronic control device with sensors have increasingly gained prominence in the last few years.
In order to be able to adapt the pressure in the high pressure accumulator, which determines the injection pressure, precisely and quickly to the respective operating conditions of the internal combustion engine, the high pressure accumulator is further provided with a pressure adjusting element or pressure control element by which excess fuel, which is not required to maintain the desired pressure in the high pressure accumulator, is fed back into the fuel tank.
The holding pressure in the pressure adjusting element is regulated by the electronic control unit of the internal combustion engine in accordance with an actual value which is measured by a pressure sensor in the high pressure accumulator and the set point value or desired value which is desired in the respective operating state of the internal combustion engine.
Since the solenoids or magnetic coils which are used in the pressure adjusting elements are made from a conductive material whose specific resistance is temperature-dependent, the current flowing through the solenoid, and thus also the armature force acting on the shut-off element, is influenced by the temperature of the solenoid. Due to the temperature-dependent resistance in the coil winding, the increase in temperature leads to a change in the current flowing through the solenoid and thus t a change in the resulting holding force in the pressure adjusting element. The holding force generally decreases because the coil materials which are used are usually conductors in which the resistance rises as the temperature increases, leading to a decrease in current.
However, since the change in the holding force of the shut-off element in the pressure adjusting element which is brought about by the temperature of the solenoid influences the pressure in the high pressure accumulator, the pressure adjusting element of the electronic control unit of the internal combustion engine must make an adjustment in order to be able to set the desired pressure in the pressure accumulator. However, this adjustment leads to a degradation of the control dynamics of the pressure adjusting element, so that the pressure which is optimum for the operating condition in the high pressure accumulator is achieved only with a delay. In order to prevent an excessively long delay in the regulation of the pressure in the high pressure accumulator, wide control range limits are generally used for prior art PI (proportional-integral) controllers for the pressure adjusting element, so that a sufficient adjustment speed is obtained during the regulation of the pressure. However, such high adjustment speeds increase the risk of overshooting when regulating the pressure, and thus adversely affect the stability of the regulating circuit. In addition, high adjustment speeds often lead to very high current peaks in the solenoid of the pressure adjusting element, which can cause damage.
The Published German Patent Application DE 195 48 278 A 1 discloses a method and a device for regulating a high pressure regulating valve connected to a high pressure accumulator. A current value which is detected in the electromagnetic drive of the high pressure regulating valve is compared with a setpoint current value which is derived from a desired setpoint pressure value. In case of a deviation, the value of the current which flows through the electromagnetic drive of the high pressure regulating valve is readjusted.